Performance limits of wearable ink-based thin-film thermoelectric generator for human-body waste heat recovery

•Performance limits of wearable thin-film thermoelectric generator are addressed.•A well-validated three-dimensional Multiphysics field coupled model is developed.•Effects of material, geometric, and environmental factors on power output are studied.•Maximum output power can reach 0.1 μW/cm2 for human-body waste heat recovery.•Optimal design criteria and multi-objective optimization are discussed and presented. Wearable ink-based thin-film thermoelectric generator (TEG) is an attractive technology for harvesting human-body waste heat and powering wearable sensors due to its advantages of good flexibility, low cost, and easy manufacture, etc. Revealing performance limits of the wearable TEG is crucial for applicability assessment and optimal device design; however, there is a lack of comprehensive and accurate performance analysis regarding material properties, geometrical parameters, and environmental factors. In this study, a well-validated three-dimensional Multiphysics field coupled numerical model is established to demonstrate the performance of a typical wearable TEG configuration, namely ink-based thin-film thermocouples connected with both-side heat dissipation fins and sandwiched by upper and lower insulation substrates. In the model, different thermoelectric materials (nano-carbon BiTe and pure BiSeTe), different insulation substrates (organic aerogel, PDMS and Kapton), different load electrical resistances, and various environmental and geometrical parameters, are considered. The results show that, (1) the thermal conductance of insulation substrates results in significant performance degradation (about one order of magnitude), indicating that previous used adiabatic condition of substrates has overestimated the TEG performance; (2) human-body thermal resistance, skin-surface contact thermal resistance, and wide-range air velocity have significant influence on TEG performance, which differ much with previous predictions under the condition of adiabatic substrates; (3) the preferred thickness ratio between upper and lower substrates is 7/8–3/2; (4) as the thickness of the whole TEG increases, the optimal thickness ratio between thermocouple and substrate decreases significantly, while the optimal thermocouple thickness is about 0.51–0.55 mm; (5) the maximum output power can reach 0.1 μW/cm2 under optimized design conditions and suitable TEG thickness. In addition, general optimal design criteria and multi-objective optimization of the TEG are disc